The present invention relates generally to optoelectronics involving optical components and, more particularly, to coupling optical components together of significantly different cross-sectional areas, such as coupling optical fibers to optical elements such as lenses, filters, gratings, prisms, and the like.
Splicing of one optical fiber to another or of one optical fiber to an optical waveguide is known. Such splicing can be done by a variety of techniques, including fusion-splicing, which involves localized melting in the region of the splice.
The following references disclose fusion-splicing of fiber to fiber or fiber to silica-waveguide: (1) R. Rivoallan et al, xe2x80x9cMonomode fibre fusion-splicing with CO2 laserxe2x80x9d, Electronics Letters, Vol. 19, No. 2, pp.54-55, 1983; (2) R. Rivoallan et al, xe2x80x9cFusion-splicing of fluoride glass optical fibre with CO2 laserxe2x80x9d, Electronics Letters, Vol. 24, No. 12, pp.756-757, 1988; (3) N. Shimizu et al, xe2x80x9cFusion-splicing between optical circuits and optical fibresxe2x80x9d, Electronics Letters, Vol. 19, No. 3, pp.96-97, 1983; (4) T. Shiota et al, xe2x80x9cImproved optical coupling between silica-based waveguides and optical fibersxe2x80x9d, OFC""94 Technical Digest, pp.282-283; and (5) H. Uetsuka et al, xe2x80x9cUnique optical bidirectional module using a guided-wave multiplexer/demultiplexerxe2x80x9d, OFC""93 Technical Digest, p. 248-249. In both cases (fiber-fiber or fiber-waveguide), the masses to fuse are very small and of similar size. The fusion does not require careful thermal balance between the two components involved and can be done with a laser beam impinging from the side.
U.S. Pat. No. 4,737,006 entitled xe2x80x9cOptical Fiber Termination Including Pure Silica Lens And Method Of Making Samexe2x80x9d, issued to K. J. Warbrick on Apr. 12, 1988, discloses fusion-splicing an undoped (pure) silica rod to a single mode fiber to fabricate a collimator, employing an electric arc. However, this is an extremely complicated method and has limited applications.
The present practice in the art often requires the attachment of optical fibers to other optical elements such as lenses, filters, gratings, prisms, and other components which have a much larger cross-sectional area than the optical fibers. The most often utilized processes for attaching optical fibers to the larger optical elements include (1) bonding the fiber faces directly to the optical element with adhesives or (2) engineering a complex mechanical housing which provides stable positioning of air-spaced fibers and optical elements throughout large changes in environmental conditions.
The use of adhesives in the optical path of such devices is undesirable due to the chance of degradation of the adhesive over time. On the other hand, spacing the fibers a fixed distance away from the optical elements by utilizing complex mechanical housings requires the use of anti-reflection coatings at all air-glass interfaces in order to minimize losses of optical energy through the device. The presence of air-glass interfaces also provides a source of back-reflected light into the optical fibers. This back-reflected light is a source of noise in many communication networks, and effectively limits transmission bandwidth of such communication networks.
In previous art, it has been shown that positioning an angle cleaved fiber or polished fiber in proximity to the angle polished face of a collimating lens results in excellent collimation and excellent performance characteristics. However, these existing technologies for assembling collimators require very labor intensive active alignment techniques. The alignment techniques include manipulating the position of the fiber relative to the lens in three linear axes and three rotational axes during final assembly. If a collimator can be built that effectively makes the fiber and the lens a single piece, then alignment can be reduced to two linear and two rotational axes during the fusion process and there is no need for alignment during final assembly, thereby reducing costs dramatically.
A key performance parameter to be minimized in collimator assemblies is back reflection of light down the fiber. By butt-coupling or fusion-splicing a fiber to a lens of the same refractive index, there is no apparent interface to cause back reflection. The beam is then allowed to diverge in the lens and does not see an index break surface until it exits the lens. By then, the beam is so diffused that the amount of light that can return to the fiber core is extremely small.
Many advances can be made in the optoelectronics and telecommunications markets if one is able to fusion-splice a single mode optical fiber directly to a collimating lens, a filter, a grating, a prism, a wavelength division multiplexer (WDM) device, or any other optical component of comparatively larger cross-sectional area. More generally, these advances can be made if one is able to fuse optical components of substantially different cross-sectional areas.
Thus, a need remains for a method of fusion-splicing optical components of significantly different cross-sectional areas.
In accordance with the present invention, such a method is provided for fusion-splicing optical components with significantly different cross-sectional areas using a laser. By xe2x80x9csignificantly differentxe2x80x9d is meant a difference of at least two times.
The method of the present invention for fusion-splicing with a laser beam two optical components, one of the optical components having a surface that has a comparatively larger cross-sectional area than a surface of the optical component, comprises:
(a) aligning the two optical components along one axis;
(b) turning on a directional laser heat source to form the laser beam;
(c) directing the laser beam to be collinear with that optical component having a smaller cross-sectional area;
(d) ensuring that the laser beam strikes the surface of the optical component having the larger cross-sectional area at normal or near normal incidence so that absorption of the laser beam is much more efficient on the surface;
(e) adjusting the power level of the laser beam to reach a temperature equal to or higher than the softening temperature of the surface of the optical component having the larger cross-sectional area to form a softening region thereon, which then softens, thereby achieving the fusion-splicing; and
(f) turning off the laser heat source.
The method of the invention is particularly useful for fusion-splicing an optical fiber to an optical element, such as a lens, having a much larger cross-sectional area In the case of the present invention, the difference in cross-sectional areas between the optical fiber and the optical element is at least about two times, and typically at least about ten times, although the present invention is not so limited.
Seamlessly fusing the optical fibers to the optical elements, as defined herein, negates the need for both adhesives and complicated housings. Additionally, such fusing eliminates the source of back-reflected light, and requires no additional anti-reflective coatings between optical fibers and optical elements. The present invention represents a substantial improvement to optoelectronic assembly, and allows such devices to be manufactured at significantly lower costs than currently achievable.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, in which like reference designations represent like features throughout the FIGURES.